The present invention relates to an electric torque converter which is arranged between a driving and a driven system.
In many drive systems, particularly those having internal combustion engines, the drive source supplies high power with good efficiency only within a narrow range and generally at high speeds of rotation. On the other hand, the driven system may often require the application of high power at very different speeds of rotation depending on the operating conditions.
While mechanical gear shifts permit a step-wise conversion of the torque, the number of steps is limited by convenience in operation and the high expense inherent therein. Infinitely variable mechanical gear shifts are limited to relatively low transferrable powers.
Hydraulic torque converters operate with infinite variation and also make it possible to operate the drive source within the optimal range of speeds of rotation. However, their efficiency is satisfactory only within a rather narrow transmission range, so that they frequently must be combined with mechanical gear shifts.
There have also been attempts to use electrical machines for speedmatching and torque conversion. These systems can be classified in different groups.
The known systems utilize the fact that the speed and torque of an electrical machine can be regulated via the magnetic field applied to the machine. These systems include generator-motor combinations in which the field of one or both machines is so regulated via resistors, additional excitation machines or current regulators that the torque or the speed of rotation can be adapted to the operating condition of the driven system.
By the use of power electronics, torque regulation has been displaced by torque controls or speed controls. The known arrangements accordingly always contain electronic control circuits and/or microprocessors or process control computers. These known systems control either the field of the machines or the current, voltage or frequency of the electrical energy applied to the machine.
Perhaps the best systems are homopolar machines which usually provide good properties for torque conversion. However, these systems disadvantageously require very high currents which occur with low voltages and must be conducted over slip rings or the like. Additionally, they require control or regulation of the torque.
The object of the present invention is to provide an electric torque converter which, with high overall efficiency without the use of components which inherently produce a loss, has a linear speed/torque characteristic even at a motor speed of zero.
Using the solution of the present invention, a change in the driven speed at optimal drive speed is possible without employing a control device, the power which may be transmitted having a wide maximum and remaining practically constant.
West German Unexamined Application for Patent No. OS 14 38 811 discloses a circuit in which an asynchronous generator attached to a turbine is connected via capacitors and rectifiers and a starting resistor to propulsion motors (dc motors). But that case is concerned with a pure starting circuit for a turbine which operates at a constant speed of rotation. In that circuit, a starting resistor for the series motors cannot be dispensed with, while the capacitors serve exclusively to compensate for stray resistances.
On the other hand, the generator of the invention produces an approximately delta-shaped alternating voltage, the dc motor is externally excited or excited by permanent magnet, and the capacitors limit the current to a permissible value, even at a motor speed of zero. Furthermore, in the case of the present invention, an additional control of the "transmission ratio" can be provided but, contrary to known proposals, this is not for the purpose of adapting the driven rotational speed at each moment to be as constant as possible relative to the speed of rotation of the drive, but serves exclusively for the overall optimizing of the total power which can be transmitted.
The solution in accordance with the present invention, furthermore, has a low power loss which increases essentially with the power to be transmitted and decreases with an increase in the driven speed.
One advantageous embodiment of the subject matter of the invention resides in the fact that the conductors of the generator winding are arranged in triangular shape on the outer surface of a stationary cylinder which can dip into the air gap of a pole wheel which is provided with a permanent magnet.
For the adjustment of small machines, West German Pat. No. 939,463 discloses an arrangement wherein a rotor with a self-supporting winding in an air gap is located between a permanent-magnet core and a return ring which is fastened by screws.
West German Unexamined Application for Patent No. OS 21 01 459 also discloses a dc motor in which operation in different speed stages (change in transmission ratio) is possible by the connecting and disconnecting of parts of the armature winding.
The present invention can be used to particular advantage in automotive vehicles since the electrical converter can replace not only the change gearing but also the clutch means.